This invention relates to the packaging of semiconductor devices, and more particularly to a package and a method for storing, assembling, or shipping semiconductor devices in expanded wafer format.
Semiconductor devices, including diodes, transistors, and integrated circuits are fabricated in large arrays of similar die on semiconductor wafers. After the processing of the semiconductor wafer is completed, the devices are tested electrically and reject die are inked for later discarding. The wafer is then scribed or sawed to separate the individual devices. The scribed or sawed wafers, now divided into individual devices, are stored, at least temporarily, before the individual die are assembled in discrete packages or hybrid assemblies. The dice may also be shipped to another location for assembly or sold as unassembled dice for eventual assembly by the end user.
There are a number of packages or containers and techniques commercially available for storing and shipping dice, but they all suffer from one or more shortcomings. With one of these, the plastic sheet upon which the wafer was scribed and broken is held about its edges by a clamping arrangement. The dice stick to the plastic sheet by electrostatic, mechanical, or adhesive forces and maintain the same approximate orientation as in the unscribed wafer. A metal plate is forced up under the plastic sheet causing the sheet to stretch. As the sheet stretches, the dice sticking to it are spread apart. The plastic sheet is then held in this stretched state by a plastic ring which fits securely about the edges of the metal plate. With the dice spread apart, the so called "expanded wafer" is convenient for handling in subsequent operations such as die bonding or visual inspection. For protection during storage, the top surface of the wafer can be covered with a sheet of plastic or other protective material. The container is thus comprised of metal plate, plastic sheet, securing ring, and the protective top sheet. This container has at least two disadvantages. First, it is expensive and second, it is bulky, being four to five inches in diameter and about one-half inch in thickness. It is inconvenient for shipping because it is heavy and has no provision for sealing the dice in the container.
Because the aforementioned container is not suitable for storage or shipping, it is common to use, in addition, a second container or die pack. A die pack is a plastic tray provided with an array of depressions of the same approximate size as the individual die to be stored. An operator transfers the un-inked dice from the expanded wafer to the die pack using tweezers or a vacuum pick up. The dice are held in place by enclosing the die pack with a tightly fitting lid. Although the die pack is a good shipping or storage container, loading the die pack is an expensive and time-consuming operation, especially when it is recalled that the dice to be stored may be only a few tens of mils on a side. It is difficult to carry out the transfer operation without damaging any of the die and without disturbing the relative geometrical orientation.
Another container technique is disclosed in U.S. Pat. No. 3,562,058. A vacuum apparatus is employed to stretch a wafer supporting plastic sheet thereby forming an expanded wafer. The plastic sheet can be held in the stretched state by vacuuming the sheet down upon a cup shaped disc covered on its upper surface with a pressure sensitive adhesive. Again, this container suffers from the same deficiencies as the first mention container. No provision is made for protecting the sensitive top surface of the dice.
Accordingly, in view of the above stated deficiencies, a need existed for an inexpensive packaging system which can be used easily and conveniently for storing, assembling, or shipping dice.